Detector or frequency changer for radio-frequency oscillations



y 7, 1948. D. WEIGHTON 2,446,118

DETECTOR 0R FREQUENCY CHANGER FOR RADIO FREQUENCY OSCILLATIONS Filed May 31, 1944 FIGJ. m I2 mm-zcr vomcs SIGNAL mrcumc I SUPPLY '4 INPUT 4,; f DEVICE H I II vlogo 25 AMPLIFIER F IG.2.

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Ewing 470M BY Patented July 27, 1948 DETECTOR OR FREQUENCY CHANGER FOR RADIO-FREQUENCY OSCILLATIONS Donaldweighton, Cambridge, England, assignor to Pye Limited, Cambridge, England, a British company Application-May 31, 1944, Serial No. 538,118 In Great Britain May ,17, 1943 The present invention relates to an arrangement suitable as a detector or frequency changer for radio frequency oscillations, particularly of very high frequency. J 5 s l i In the paper by Tonks and Langmuir. entitled "Oscillations in ionised gases. published in. the Physical Review for February 1929\and thepaper bySluz kin and Maydanov entitled Factors determiningthe intensity or oscillations in the plasma of gaseous dicsharge published in the Journal of Physics of the U. S. S. R. 1942,, it has been. disclosed that certain oscillationsof very high frequency mayoccur in. the plasma of a gaseous discharge and in particular it has been shown that the elections will respond to oscillations which are too rapid for the ionsto follow.

The present invention consists in an arrangement suitable as a detector or frequency changer, in which a gas discharge tube is employed as the non-linear element and oscillations of the electron plasma of the gaseous discharge areexcited by a radio frequency voltage superimposed on a potential applied to the tube to maintain the discharge. The discharge is maintained by an external source of supply, which may 'be a direct potential, or alternatively in the case of a frequency changer, the direct voltage supply may be dispensed. with and the discharg mantained by a potential derived from the local oscillator of the frequency changer.

In theaccompanying diagrammatic drawings, Fig. ,1 depicts the circuit arrangement used as a detector.

Fig. 2 similarly depicts the arrangement used as a frequency changer.

Fig. 3 illustrates a matching device suitable for employment in the circuits of Figs. 1 and 2, and

Fig. 4 illustrates a modified form of gas discharge tube that may be employed.

Referring to Figs. 1 and 2, the radio frequency signal input is fed to a gas discharge tube iii, such as a neon tube, by an impedance matching device indicated at I I The discharge of the tube I is maintained by a direct voltage supply applied through a resistor i2. When the arrangement is used as a detector, as in Fig. 1, the rectified voltage is developed across a load I3 connected in series with the tube and fed to a video amplifier indicated at M. The mean current passing through the discharge tube It) may be adjusted to the condition Where the electron plasma is most sensitive to an impressed voltage of the frequency which it is desired to detect; or if it is desired to obtain a maximum signal to noise ratio when working at very low input levels, the dis- 4 Claims. (01. 250-27) charge tube may be adjusted to a different optimum condition, since the random noise generated by the discharge varies with theion density. Thus, the current for optimum signal: to noise ratio is in general different from that required for optimum sensitivity.

When the arrangement is used as a frequency changer, as in Fig. 2, an alternating voltage of suitable frequency derived from. a local oscillator indicated at 15 is also appliedby a suitable coupling Hi -to the tube l0, and the load [3 of Fig. 1, is replaced by an inductance l1 forming part of, a parallel resonant circuit tuned to the interme diate frequency, the output from which is fed, in this case, to an intermediate frequency amplifier depicted at [8. In some cases, it may be advantageous to dispense With the direct voltage'supp-ly at It, and this can be done provided that suiiicient power is available from the local oscillator [5 to maintain the discharge in the tube I0;

The matching device I! may be of the character illustrated in Fig. 3, consisting of a resonant concentric line comprising outer conductor l8 and inner conductor 25!. The signal input is tapped into the line at a suitable distance from the adjustable tuning bridge 2|. The gas dis charge tube In is arranged in the end of the concentric line, as illustrated, the screening enclosure 22 enclosing the portion 24 of the outer conductor 9 which contains tube Iii. The screen 22 is connected the outer conductor 19 and constitutes.

in effect, an extension of that conductor and serves to prevent high frequency losses. The portion 24 is insulated, for low frequencies, from the screen 22 and conductor 19 by suitable insulation 23, such as mica. The electrodes of tube II] are connected respectively to the inner conductor 29 and outer conductor portion 24. The arrangement of screen 22 around outer conductor portion E l together with the insulation 23 provides the capacity indicated at 25 in Figs. 1 and 2.. The resistor l2 (Figs. 1 and 2) through which the direct voltage bias is supplied is connected at a point of the circuit which is at earth potential with respect to radio frequencies.

Fig. 3 also illustrates one embodiment of gas discharge tube Ill suitable for carrying out the invention, in which the electrode structure consists of a cylindrical cathode 2'! and an axial rod 26 as the anode, the tube being arranged with its electrodes coaxial With the concentric line, as illustrated. The cathode is activated to supply the primary electron stream and may be either cold or heated. The tube is filled with a suitable gas, such as neon, at a suitable low pressure.

The electrode leads are brought out from one end of the tube conveniently for connection to the end of the concentric line, the anode 26 being connected to the inner conductor 20 and the cathode 2,! being connected to the outer conductor l9; The use oftube M in the concentric line with the tube electrodes concentric with the inner and outer conductors of the line has the,

cathode being activated and either cold or heated and the tube having a filling, such as neon, at

suitable low pressure. conveniently brought out axially at opposite ends of the tube for connection to the end of the concentric line, so that the leads are coaxial with the line. Compared with the electrode structure of the tube in Fig. 3, the electrode structure of the tube of Fig. 4 has the advantage of reduced capacity and better performance in the input circuit to the video or intermediate frequency amplifier.

I claim:

1.,Arrangement for detection and frequency changing in ultra highfrequency signalling systems, comprising in combination, a gas discharge tube having an envelope containing a low pressure gas filling and electrodes therein consisting of a cylindrical cathode concentrically surrounding and spaced from an axial rod anode, impedance matching means iorfeeding an ultra high frequency signal input to said tube, said means comprising a resonant concentric line having an outer conductor and an inner conductor, said tube being disposed within said outer conductor with said anode and cathode coaxial with said line and respectively conductively connected to said inner conductor and said outer conductor of said line, and means for applying an isonising potential to said tube to maintain a discharge therein such that ultra high frequency oscillations of the electron plasma of such discharge are excited responsively. to the impressed signal input frequency.

2. Arrangement for detection and frequency changing in ultra high frequency signalling systems, comprising in combination, a gas discharge The electrode leads are 4 tube having an envelope containing a low pressure gas filling and electrodes therein consisting of a cylindrical cathode concentrically surrounding and spaced from an axial rod anode, impedance matching means forfeeding an ultra high frequency 'signalinput to said tube, said matching means comprising'a resonant concen- .tric line having an outer conductor and an inner conductor and means including a short-circuiting member within'one end of said outer conductor and bridging said conductors and being adjustable axially therealong for tuning said line, means for applying 'an ultra high frequency signal input tosaidline at a point spaced from said end thereof and from said short-circuiting memher, said tube being located within the other end of said' outer conductor with said anode and said cathode disposed coaxially with said line and respectively conductively connected to said inner conductor and to said outer conductor of said line, and means for applying an ionising potential to said tube electrodes to'maintain a dis-- charge in said tube such that ultra high frequency oscillations of the electron plasma of such discharge are excited responsively to the impressed signal input frequency. v I, J 3. Arrangement as defined in claim 1, said means for' applying ionising potential to said tube comprising a local ultra high frequency oscillator.

4. Arrangement as defined in claim 2, said means for applying ionising potential to said tube comprising a local ultra high frequency oscillator DONALD WEIGHTON.

' REFERENCES CITED 7 The following references are of record in the file of this patent:

UNITED STATES PATENTS Dallenbach et a1. Aug. 14, 194E 

